1. Field of the Invention
The present invention relates to a method and a device for measuring a mechanical characteristic of a long metal product, a method of continuously producing a long product and the long product obtained. The invention applies in particular to the manufacture of long steel rods and wires having round or other shaped cross-sections.
2. Discussion of the Background
Manufacturing long products such as wires or small section rods is known per se. For example, a method of rolling or drawing is known, in which the long product moves continuously through the rolling or drawing installation to the exit from the installation where the long product can be wound, for example into the form of a spool or a coil, or is in the form of a rod.
Flat products such as strips can also be manufactured continuously, for example by rolling. Although such products are not usually designated long products, this term as used hereinafter refers equally to narrow flat products to which the invention is applicable.
Manufacturing austenitic steel wires of precisely specified diameter by drawing a machine wire or a rod through one or more successive dies of decreasing diameter to reduce its diameter is known. Traction is applied to the wire on leaving each die by a capstan. The wire may undergo the various drawing operations in a totally continuous manner by passing successively through the dies or in a series of steps after each of which an intermediate product is obtained that is drawn to a smaller diameter.
Manufacturing by drawing austenitic stainless steel wires where the metastable austenite is converted partly or totally into martensite because of plastic deformation is also known. Such wires, the tensile strength of which can be as high as around 2000 MPa, have various uses and in particular can be used to manufacture springs.
Wires of this type, obtained in the form of a spool or a coil after the drawing operation, have mechanical characteristics that depend not only on the chemical composition of the steel but also on the drawing conditions. To guarantee highly regular mechanical characteristics of the wire, the sample on which tensile tests are carried out is taken from the end of each spool or coil or from a wire portion obtained by means of a test drawing operation. The drawing conditions, and in particular the drawing speed, are adjusted in the light of the results of such tests either for a series of spools or for each spool. This procedure, possibly complemented by a final sorting of the spools or coils, guarantees that the tensile strength obtained is in a range of 100 MPa around the target value. This range, generally accepted and imposed by the usual standards, is sometimes deemed to be too high, and it is desirable to reduce it. The only known way of doing so is a more severe sorting than is usually practiced.
When such wires are used to manufacture coil springs, the geometry of the springs obtained is found to vary, not only when the wire is taken from different spools or coils but also when it is taken from the same spool or coil. It is then necessary to sort the springs and to reject those that do not have a satisfactory geometry.